The invention relates to a stripping device for the return run of conveyor belts, which device consists of an adjustable, stationary or of an elastically supported carrier transverse to the direction of travel of the belt and of several stripping elements which are each held at feet and which are held adjacent to one another, if necessary in two rows, at the carrier and each carry a stripping lamella or a stripping blade which is held with the aid of a stripping body and is supported hinged and elastically by a torsion spring between each foot and this stripping body, in which, if necessary, the foot of a perpendicular dropped from the hinge to the stripped belt section is located, in the direction of belt travel, at a distance from the point of contact between the cutting edge of the stripping lamella or of the stripping blade and the belt section, which, at a maximum, corresponds to half the distance between the hinge and the belt section and in which, if necessary, the distance between the hinge and the belt and the parallelity of the stripping edge with respect to the belt section can be adjusted at each stripping element.
Such stripping devices have been known for a long time and have been very successful in the most difficult stripping tasks. The peeling cleaning effect in conjunction with an undelayed evasion movement of each stripping element in the case of contaminations which solidly adhere to the belt or in the area of joints results in very good cleaning with extreme belt care. However, these excellent characteristics are fulfilled only if the individual stripping elements are correctly adjusted, that is to say the stripping edge extends essentially in parallel with the belt surface and the contact pressure has the predetermined magnitude.
In most conveyor belts used for transporting bulk material, the centre areas are more soiled than the outer edge areas. In consequence, the cleaning performance of the stripping elements arranged in the centre area is greater and thus more wear-intensive. As a consequence of this phenomenon, the individual stripping elements must be readjusted from time to time with respect to the belt surface concerned since an overall displacement of the carrier carrying the stripping elements is too gross; with such a readjustment, that for the stripping elements arranged in the centre area would be too little and for the stripping elements close to the edge regions it would be too much. Individual adjustment is performed by displacing each stripping lamella with respect to the stripping body carrying it.
In the known stripping device, the said parts are connected with the aid of a bolt and a stop nut, the screw bolt being secured against twisting due to the construction of the stripping body. However, readjustment at this location is very difficult since the amount of adjustment is frequently very difficult to estimate and accessibility is frequently greatly impeded. In particular, the new setting found can be lost again when the stop nut is tightened again unless the stripping lamella is specially held.
The invention has the object of proposing a stripping device of the type initially mentioned, with the application of which readjustment with respect to parallelity and/or distance of each stripping element from the belt surface to be stripped is much simpler or is performed automatically according to further developments. In addition, the behaviour of the device in the reversing mode of operation is intended to be improved with particular developments.
To achieve this object, the invention proposes that, for setting up parallel with respect to the belt, each stripping element can be swivelled about an axis which forms an angle .alpha. of less than 90.degree. with the belt surface, on the side of the belt facing the strip ping element, the apex of which angle .alpha. is the point of angle .alpha. which is farthest along in the direction of belt travel.
The specified angle .alpha. can assume approximately any value between 0.degree. and 90.degree.. For better understanding of the position of angle .alpha., angle .alpha. should be imagined as a solid structure having two legs, one leg coinciding with the underside of the belt and the other leg lying on the said axis. The apex then resulting is the point of the angle which is farthest along in the direction of belt travel during the cleaning operation. No other point of the angle along the legs reaches this extreme position.
Due to the inclined position of this axis, a swivelling movement of the stripping element in one or the other direction leads to a type of rocking motion of the stripping edge of the stripping lamella so that one edge of the stripping edge drops or rises compared with the other one with increasing swivelling away from the centre position. The desired parallelity between the stripping edge of the stripping lamella and the belt surface can be established on the basis of this phenomenon.
In particular simple embodiments of a stripping device according to the invention, this adjustment is performed manually by swivelling and securing the entire stripping element at an accessible point. With clever design, the location of the adjustment is located adjacently to or even below the carrier on which all stripping elements of a row are mounted. If a flap is used on each stripping element, this area is also not contaminated as a rule.
An embodiment is particularly advantageous in which the adjustment of parallelity between the cutting element and the belt surface is automatic. For this purpose, the swivellable support is left to itself, limits being predetermined, if necessary, with the aid of stops so that the stripping element is not aligned unchecked when the belt starts to travel from standstill. It is assumed that the belt has a stretched section which has the effect of a curvature and thus a change in the parallelity required until then. As a control input to the self adjustment, there is then firstly a pressure by the belt on one corner of the cutting edge whilst the opposite corner is relieved. In consequence of a rotation of the stripping element about the adjustment swivelling axis, the loaded corner thereupon escapes downward, because of the inclined position with respect to the belt surface, and in the direction of belt travel whereas the relieved corner is moved upward and against the direction of belt travel. This movement is concluded when both corners again rest against the belt surface with the same loading.
Depending on the amount of inclination, that is to say depending on the size of the angle .alpha., the change in parallelity is great or less great. It must be selected in such a manner that a stable contact is produced between the friction couples used, that is to say between the lamella edge and the belt material and no pendulum oscillations are created. Tests may have to be made to produce the optimum position. Although the lamella edges are basically produced of a highly wear-resistant material, constructions both in hardened steel and in hard metal are customary which clean belt materials of the most varied qualities.
Concerning the position of the swivelling axis in a stripping device according to the invention, it should be said again, that in the side view, the axis imagined to be extended up to the belt surface to be cleaned touches the belt, so to speak as a tractory, that is to say is inclined in the direction of belt travel. It is unimportant in this connection whether the axis intersects the belt plane in front of or behind the cutting edge of the stripping lamella, only the correct inclination is of importance. In completed plants, the swivelling axis can traverse the centre axis of the torsion spring or be located in front of and behind this centre axis. It is also unimportant whether the swivelling axis is realized in the area of the stripping body, that is to say for example between stripping body and lamella or is formed as swivelling connection between the foot of the stripping element and the stripping body, that is to say below the torsion spring hinge. Naturally, a hinged connection between the foot and a component mounted on the carrier can also be considered. The important factor is always the correct inclination of the swivelling axis which leads to an angle .alpha. of 75.degree. to 45.degree. in examples constructed. Naturally, this value can also be higher or lower in extreme cases of application.
As a swivelling connection, in particular, a sleeve and a bolt are available and it is unimportant with which component the sleeve and which component the bolt is associated. In deviation from this, roller bearings can also be provided which is always the case when a particularly sensitive adjustment is desired because, for example, the swivelling axis is relatively steep (.alpha. in the vicinity or equal to 90.degree.) or the fluctuations to be expected occur only for brief periods, that is to say a particularly rapid realignment of parallelity is required.
It has already been mentioned initially that an individual height adjustment of the stripping element compared with the belt surface is frequently also desirable, In the case of simple illustrative embodiments, the height adjustment can coincide with the adjustment of parallelity in such a manner that a swivelling is achieved by loosening a bolt secured with two nuts and a different height position is achieved by screwing the nuts up and down along the bolt. In this arrangement, the height adjustment occurs along the axis about which the swivelling for adjusting parallelity also takes place. Adjusting the height in this manner at a slight angle compared with a perpendicular dropped to the belt surface is harmless. Naturally, this height adjustment can take place independently of the adjustment of parallelity and depends on the operating conditions occurring. If, for example, the stripping element is used immediately in the area of a reversing roller of the conveyor belt, fluctuations in parallelity are not very likely. In this case, adjustment of the parallelity between the cutting edge of the stripping element and the belt surface can be omitted. However, a height adjustment may quite well be desirable because of the different amount of wear of the individual stripping elements over the entire belt width.
It is particularly suitable to construct the linear adjustment for setting the height position or for the contact pressure of the stripping lamella against the belt surface in elastic manner so that any possible wear at the stripping lamellae corrects itself automatically. To implement this principle, a component connected to the stripping element, particularly a foot constructed as a bolt, rests against a rubber spring, a steel spring or a constructed or encapsulated gas spring. Details of such illustrative embodiments will be explained in greater detail in conjunction with the description of the figures. The important factor is the finding that the axis of the displacement for the height adjustment extends essentially vertically with respect to the belt surface, that is to say does not been described in conjunction with the parallel adjustment.
The reason for the axis of the direction of displacement for height adjustment having to extend approximately vertically with respect to the belt surface lies in the fact that an inclined position in the sense of the swivelling axis for the adjustment of parallelity would lead to a force component which would attempt to lift the stripping element. This force component would result in too high a height position or contact pressure force and, above all, prevent the stripping element from dropping back into its initial position if, as a result of an obstinate contamination or as a result of projecting parts, for example in the area of joints at the belt surface, the stripping element is violently deflected against the effect of the torsion spring so that it temporarily lifts away from the belt surface. In this brief period of lifting away, the spring lifts the stripping element as a whole. When the stripping lamellae again come to rest against the belt surface, the stripping element is pressed back into its nominal position if the axis for the height adjustment is correctly aligned whereas, in the case of an inclined position, this raised position will be largely retained due to the force component mentioned.
Independently of a manual or automatic parallel adjustment or height adjustment, it is suitable in particular cases to design the stripping element to be rotatable about an axis which extends essentially vertically with respect to the belt surface. If a height adjustment along an axis is provided, the axis of rotation can coincide with the axis for the height adjustment. Rotation of the entire stripping element about the axis of rotation is used during reversing operation, that is to say if the belt is used in both directions of travel. Free rotatability of the stripping element leads, after standstill and restart of the belt in the opposite direction, to the stripping element rotating in due course by 180.degree. about the abovementioned second axis so that a stripping effect also exists in the reversing mode of operation. For these cases of application, it must be assumed that appropriate stripping devices are arranged at both discharge ends which can be of identical design.
Although the stripping element according to the invention in its original design is particularly well suited to reversing operation even without such rotation since the torsion spring allows the stripping body with the lamella attached to it to "fold through" which produces a trailing effect with very high belt care, this reversing position of the stripping element without rotation has the striking disadvantage that, despite the running-in which forms between the stripping lamella and belt surface, a certain cleaning effect is produced so that the entire rear of the stripping element is highly soiled after having been operated in reversing mode for a relatively long time. This is particularly undesirable because it is not as easy to take protective measures at this location. If, in contrast, the stripping element rotates by 180.degree. as provided in accordance with the said development, a stripping effect is produced in reversing mode on the side provided for this purpose so that the measures taken for protection against soiling are fully effective.
It has already been pointed out above that this characteristic of free rotatability can be used independently of all other characteristics hitherto described. Naturally, combined use is also possible, that is to say also in conjunction with a swivelling movement about an inclined axis for setting up parallelity and in conjunction with a height adjustment, however this is designed. The type of actuation--manual or automatic--is also freely selectable. It is of importance that the free swivellability of a stripping element for setting up parallelity about the inclined axis does not produce a rotation by 180.degree. during a reversal of the direction of travel of the belt since such a rotation would involve too violent a disturbance of the belt path. Swivelling over at this point can be easily prevented with the aid of a swivel limit of the parallelity adjustment.
The same principles are used for constructing a swivellable support as have already been described in conjunction with the swivelling movement for achieving a parallel alignment of the stripping edge to the stripping lamella with respect to the belt surface. A repetition can here be omitted. It also applies to this swivelling connection that it can be laterally limited if a rotation by 180.degree. in reversing mode is not desired but the automatic height adjustment is constructed as a sleeve-bolt link.
The evasion movements of the stripping elements can be very violent, particularly in the case of very rapidly travelling belts, so that they briefly lift away from the belt surface and subsequently come to rest again against the belt surface. At these instants, each spring for correcting wear is without counterforce, with the consequence that the stripping element is raised by a certain amount. Such raising can be undesirable since the stripping element then initially operates with an unfavourable contact angle. To avoid the lifting, the invention, in a development, proposes a hydraulic damping of the spring which can be particularly easily implemented in conjunction with an encapsulated gas spring. In that case, there are only very slow positional changes along the axis of adjustment which are capable of tracking any wear but largely leave out movements which would be possible due to a short-term interruption in counterforce. Similarly good spring and damping characteristics are obtained if a piston cylinder unit is used as spring in which the hydraulic medium is loaded by a gas cushion. Almost any damping characteristic can be freely selected due to the hydraulic guidance. Such hydro-pneumatically guided and adjustable stripping elements, however, are suitable only for special tasks due to the high costs.
To implement the inclined position of the axis for setting up parallelity, it is particularly suitable to provide a carrier of a tube to which lugs having one drilled hole each are for example welded laterally at predetermined distances approximately with the desired inclination and to which the respective guide and fixture of each stripping element is attached. With lateral clamping in corresponding holders, the tubular construction of the carrier enables twisting about the longitudinal axis by means of which, if necessary, the inclination of the adjustment axis can be corrected or set up. A possible change in distance from the underside of the belt can be very easily compensated by the holders for holding the tube ends being adjusted correspondingly which, as a rule, is very easily possible since these holders are held on threaded spindles which are anchored on the conveyor belt structure. The axial inclination can be individually adjusted in this manner.
In deviation from this, instead of the lug, a sleeve can be, for example, welded in each case into the tubular carrier which fulfils the same purpose, only the threaded bolts or threaded sleeves penetrating through the sleeve must then be constructed to be slightly longer.
Finally, a common spring can be provided for the stipping elements of a single carrier, in the form of a pneumatic spring which is located inside the tubular carrier if the individual stripping elements are guided in such a manner that the free ends of the feet point into the inside of the tubular carrier and rest on the spring. The hardness of the spring effect can be determined by an appropriate pressure loading. In deviation from this, each foot can be used in an essentially gas-tight guide as piston which is displaced by the tube carrier when the inside of the tube is loaded with a corresponding gas pressure.